As one of audio coding techniques to compress and expand an audio signal of voice, music, or the like, there is a spectral band replication (SBR) technique. The SBR technique is a technique in which an audio signal is compressed by reproducing a high-band component from a low-band component. The SBR technique is a technique that enables coding with high sound quality at a low rate and therefore is used for various use purposes.
In audio coding, the SBR technique extracts a low-band component from an input sound source and extracts envelope information and tone information from a high-band component for information amount compression. The SBR technique replicates the low-band component to reproduce the high-band component. The envelope information is used for correcting the magnitude of energy of the high-band component reproduced through the replication. On the other hand, it is difficult to reproduce a signal that exists only in the high-band component through the replication of the low-band component. Thus, the SBR technique acquires information relating to the frequency and the magnitude of the energy about a tone signal that exists only in the high-band component as the tone information. The tone signal is a signal with a single frequency that is artificially given. The tone signal that exists only in the high band is included in music or the like performed by an electronic musical instrument. At the time of decoding, the tone signal is added based on the tone information to the high-band component reproduced with the envelope information and thereby the high-band component may be accurately decoded. For example, a technique using the SBR is disclosed in Japanese Laid-open Patent Publication No. 2008-96567.